Plastics are inexpensive and durable materials, which are employed to manufacture a variety of products that find uses in a wide range of applications. As a consequence, the production of plastics has increased dramatically over the last decades. Among them, one of the largest groups is the group of polyolefin-based plastics. For instance, in Europe, polyolefins represent nearly half of the total volume of the plastics produced. Indeed, polyolefins may be used in a wide range of applications, including packaging (e.g.; trays, containers, bottles, bags, etc.), blown films (e.g.; bags and sacks), clothing field (e.g.; under garments for wetsuits), agricultural industry (e.g.; mulching films used to cover seeds or planted seedlings, silage films), etc. Polyolefin polymers that are most often used include polyethylene (PE) and/or polypropylene (PP), because of their low cost and mechanical properties adapted to almost all applications.
About 40% of polyolefin-based plastics are used for single-use disposable applications, or for short-lived products that are discarded within a year of manufacture. Because of the durability of the polymers involved, substantial quantities of plastics are piling up in landfill sites and in natural habitats worldwide, generating increasing environmental problems. As a consequence, more than 100 million tons of plastic wastes per year are produced, that predominantly contain polyolefins that end up as litter in the environment. Conventional polyolefins are considered as highly resistant to biodegradation, because of their high molecular mass values, hydrophobicity, crystallinity and lack of chemical functions such as alcohol, ester and acid, so that they may persist in the environment for decades, increasing environmental problems.
Different physical, chemical and/or biochemical approaches have been developed to reduce the biodegradation resistance of polyolefin-containing plastics. For instance, plastic articles made from a mix of polyolefins and biodegradable polymers, which may be natural (e.g., starch or cellulose) or synthetic, have been proposed. However, such kind of mixed plastic is both expensive, not easily processed, and exhibits weak mechanical properties. Moreover, only the biodegradable part of the corresponding mixed plastic article is degraded, the polyolefins remaining essentially non-degraded. An alternative to conventional, bio-inert polyolefin-containing plastics has also been developed using oxo-(bio)degradable polyolefins. However, the complete degradation of such plastics requires a two-stage process, involving oxidative degradation followed by the biodegradation of the oxidation product (for example alkanes, alcohols, aldehydes, esters, lactones, ketones and hydroperoxides). Up to now, there is no evidence that natural environmental conditions can allow biodegradation of oxo-degradable polyolefins up to carbon dioxide, water and biomass and it seems, to the contrary, that such oxo-degradable polyolefins are fragmented into smaller parts that still persist in the environment in a reasonable time allowing the non accumulation of degradation products.
There is thus a need for polyolefin-containing plastics having improved biodegradability that may be entirely degraded, under conditions generally encountered in the natural environment and/or in biodegradation process.